This invention relates to methods and apparatus for inspecting residual liquid such as water, oil, and liquid soap in empty washed food and beverage containers, in particular, refillable beverage containers.
In general, it is desired to reuse food and beverage containers for economical sake and required to wash the containers with water or soap to remove residual liquid or dirty things therefrom before the containers will be refilled with food or beverage. After the washing processes, since remaining liquids such as water, oil, and liquid soap may exist further in the containers, these residual liquids should be completely detected and removed before the refilling processes.
Furthermore, beverage containers returned back to a refilling factory from sellers and markets may be contaminated with residual cooking oil and motor oil. Such containers have to be disposed of before their washing processes because these materials are difficult to remove completely in conventional washing processes and, in fact, the washing processes may spread these materials to other containers.
To reject such containers containing excess water or oil, the refillable beverage containers are normally detected in two positions in a container process line by using electro-optic inspectors.
U.S. Pat. No. 4,221,961 discloses one of electro-optic inspectors, in particular, a bottle inspector. The known bottle inspector is so constructed that it can detect particles and liquid in a bottle. It has a light source located under the bottle bottom, a rotatable scanner head located over the bottle neck to receive light passing through the bottle bottom from the light source, and a detector for receiving light reflected by the surface of the scanner head to detect only particulate matters on the bottle bottom. The scanner has reflecting segments and non-reflecting portions. The reflecting segments reflect the light passing through the bottle bottom so as to focus a bottle bottom image onto the detector. If there are particulate matters on the bottle bottom, they block the light from the light source to cause a dip in detector output. The non-reflecting portions are provided with an infrared detector for detecting the infrared radiation passing through the bottle bottom. The light to be received by the infrared detector is filtered so that only light having wavelengths in or near one of the absorption bands of liquid can pass therethrough to reach the infrared detector. If there is liquid in the bottle bottom, the light is partially absorbed to cause a dip in A.C. coupled amplitude of the infrared detector providing an indication of the presence of the liquid.
This is liquid detection is based on the fact that the light in the near infrared wavelength range is greatly absorbed when it passes through liquid such as water, oil or the like. However, the light from the light source is also absorbed by a bottle wall in addition to the liquid in the bottle. Optical transmittance varies also with thickness or color of the bottle wall as well as kind or quantity of liquid. In case that the quantity of liquid is very small, the thickness or color of the bottle wall may have more influence on the optical transmittance than the presence of liquid. For this reason, the known detector can detect the presence of liquid in only the case of relatively large amount of liquid existing in the container. Because, at this time, other interfering components such as the bottle wall will be able to be neglected. However, a small quantity of liquid cannot be effectively detected by means of the known detector for the above reason. Even if the quantity of liquid such as water, oil or liquid soap in the bottle bottom is small, it affects human taste sensitivity and food or beverage quality in the containers. In addition, the oil or soap may cause a health hazard.